Newman LA (2006) Comparison of the effects of selective cholinergic or noradrenergic deafferentation in the medial, prefrontal cortex on sustained attention. Neuroscience 2006 Abstracts 369.21. Society for Neuroscience, Atlanta, GA.
Summary: Acetylcholine (ACH) and norepinephrine (NE) have been shown to be critically important in controlling the activity of cortical neurons during attention demanding tasks. ACH efflux increases during performance of a sustained attention task and the introduction of distracting stimuli augment this efflux (Himmelheber, Sarter and Bruno 2000). Electrophysiological recordings in NE cell bodies in the locus coeruleus show an increase in tonic firing when distracting stimuli are presented during an attentional task (Aston-Jones and Cohen 2005). The current study assesses the effects of neuroanatomically discrete depletions of these neurotransmitters in the prefrontal cortex (PFC) on a sustained attention task. Male, Long Evans rats received either sham (SHAM), cholinergic (ACH LX) or noradrenergic (NE LX) lesions of the medial wall of the PFC by injections of vehicle, 192 IgG saporin or dopamine beta-hydroxylase saporin respectively. Rats were trained to detect brief, temporally unpredictable, visual cues of varying duration (500, 100, 25 msec) and discriminate these events from non-signal trials. Several manipulations were run to vary the attentional load of the task. These manipulations include a tone with a predictable on-off pattern or a tone with an unpredictable on-off pattern. Preliminary results suggest that NE LX rats were more vulnerable than SHAM or ACH LX rats to the detrimental effects of the unpredictable but not predictable tone. These data suggest that NE is critical to filtering unpredictable distractor stimuli. Additionally we tested the effects of disrupting the temporal contiguity between correct responses and reinforcement as this has previously been shown to increase NE efflux in the frontal cortex. All animals were impaired by the introduction of a variable delay between a correct response and the delivery of a food reinforcer, however NE and ACH lesions of the PFC augmented this impairment. This suggests that both neuromodulators are critical in maintaining performance when reinforcer predictability changes. Manipulations of event rate, event asynchrony, signal probability and the dynamic stimulus range will also be discussed.
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